Throughout the World Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen. In areas with poor sanitary conditions C. trachomatis causes trachoma the most common cause of preventable blindness in the World. In symptomatic cases, unless therapy is implemented in a timely manner, long-term sequelae including, pelvic inflammatory disease, chronic abdominal pain, ectopic pregnancy and infertility, may develop. In addition, a majority of the genital C. trachomatis infections in women are asymptomatic, therefore are not treated, and as a result chronic complications can arise. Thus, the only practical approach to control chlamydial infections is by vaccinating the population at risk. In this proposal we want to test the hypothesis that a vaccine formulated with recombinant C. trachomatis antigens can protect female mice against a genital challenge. To this end we are going to express, purify and test 20 C. trachomatis antigens identified during Phase I of this proposal. To express chlamydial antigens we plan to explore two different methods: the conventional Escherichia coli expression system and the E. coli based cell-free expression system that ImmPORT Therapeutics, Inc. utilized to express the chlamydial ORFome for Phase I. We will first test these recombinant antigens in Balb/c mice using systemic and mucosal routes of immunization formulated with adjuvants that favor a Th1 and a Th2 response. The mice will be challenged in the genital tract at four weeks following the last immunization. Parameters of protection will include: percentage of mice with positive vaginal cultures, severity and length of vaginal shedding and histopathological changes in the genital tract in particular hydrosalpinx formation. The antigens that induce protection will then be tested in C3H/HeN and C57BL/6 mice. Our goal for this Phase II is to identify a group of 3-4 recombinant chlamydial antigens that protect mice against a genital challenge. An efficacious vaccine against C. trachomatis will have a tremendous health and economic impact throughout the world. PUBLIC HEALTH RELEVANCE: Throughout the World Chlamydia trachomatis is the most common sexually transmitted bacterial pathogen. In areas with poor sanitary conditions C. trachomatis causes trachoma the most common cause of preventable blindness in the World. In symptomatic cases, unless therapy is implemented in a timely manner, long-term sequelae including, pelvic inflammatory disease, chronic abdominal pain, ectopic pregnancy and infertility, may develop. In addition, a majority of the genital C. trachomatis infections in women are asymptomatic, therefore are not treated, and as a result chronic complications can arise. Thus, the only practical approach to control chlamydial infections is by vaccinating the population at risk. In this proposal we want to test the hypothesis that a vaccine formulated with recombinant C. trachomatis antigens can protect female mice against a genital challenge. To this end we are going to express, purify and test 20 C. trachomatis antigens identified during Phase I of this proposal. Our goal for this Phase II is to identify a group of 3-4 recombinant chlamydial antigens that protect mice against a genital challenge. An efficacious vaccine against C. trachomatis will have a tremendous health and economic impact throughout the world.